Eyes Flashcards
Eye anotomy
(fluids)
There are 2 areas of fluid which give the eyes their shape.
- Vitreous humor (back)
- Aqueous humor (front)
Eye anotomy (front)
Cornea - transparent layer protecting the eye on the ouside. Allows light to enter the eye and fall on th lense via iris
Iris - coloured area that changes size depending on the amount of light going throu it via the pupil. In low light, they enlarge. In bright less they are smaller.
Lens - located byhind the iris and changes change/stretches with assistance of ciliary muscles, to control focus. the greater the curvature, the greater the focus (occurs at a near object)
Eye anotomy (back)
Retina: Light focused by the lense on a light-sensitive membrane
In the Retina, there are Rods and Cones photoreceptors connected to nerve cells
the most sensitive area of the Retina is Fovea because it has lots of ‘cones’ only
Rods and cones are not distributed evenly
What are Rods
dark-seeing
help with peripheral vision
sensitive to movement
seeing in low light
not colour sensitive (only grey, blacks, whites)
located outside the foveal
What are Cones
Light seeing - help with seeing in bright light / daylight:
- colour sensitive
- seeing in detail
- distant objectives
located in the central section of the retina (foveal)
Visual interpretation
Retina converts the focused light into electrical impulses that reach the lower end of the brain and then routed to the visual vortex to interpret the info received from both eyes.
This info is then passed on to the cerebellum via the optic nerve, which helps us control movment and balance.
What is Field of View
it’s the portion of the world we see with each eye (monocular vision) when stationary
usually 120 degrees Horizonal
150 degrees vertical
What is the field of view when using binocular vision
there is an overlap of field of view at 60 degrees from the centre of the field
What is the blind spot
In the binocular vision in each eye there is an area in the retina without rodes or cones(light sensitive cell) ‘5 degrees blind spot’ - it’s usually where the optic nerve leaves the eyeball.
the info/image missing in one eye’s blindspot is compensated by what the other eye sees - hence you need binocular vision.
“must move your focus of attention frequently to scan your surroundings’
what is central vision
in the Fovea, there is an area of cone vision (1 degrees) that has the most visual acuity
Peripheral vision
area that detects movement but can’t distinguish details (you will see it best you move your sight to the sides, as opposed to centre in dark light)
what is binocular vision and its benefits
Binocular: using both eyes to focus
Benefits:
Eliminate risk of blindspots
Can see depth better: when looking at an object, each eye receives light from the object at different angles. The 2 images help the brain determine the distance of the object. The difference in both objects is greater when close vs far.
see in 3D
What kind of vision (binocular or monocular) gives us depth and distance
binocular
Types of depth and distance illusions
Parallax
head movements cause distant objects to appear to move relative to each other
Perspective
converging parallel
Relative size
Distant objects look small/closer objects look large
Relative motion
Distant objects appear to move slow/ closer objects appear to move fast
Overlapping motion
object in front of another appears closer
Aerial perspective
Distribution of light at a distance makes objects look blue
How to protect the eyes from bright light
Eyes take a wide range of light conditions ranging from light to dark
High energy lights - blue and ultraviolets found at high altitude
Bright light is dangerous due to high UV wavelength. The effectds are cumulative and can lead to blindness
Use 100% UV protective sunglasses
high quality optical glass
impact resistant
thin frames
reduce glare and increase contrast in the dark
avoid photosensitive glasses as they don’t adapt to changing lights
avoid polarised glasses as they can conceal important colours in the instruments you use
Affects of Dim light on the eye
DARK ADAPTATION
Dim lights reduce the resolution of objects, especially at a distance because cones don’t work in dark light and generally need brightt light to focus.
the pupils try to dilate to allow more light in (this takes seconds) but the Cones take 9 min and** rods take 30 min to fully adapt**
*anything affecting vision like hypoxia usually is more noticeable at night, even if below 10,000 ft)
Night vision can deteriorate at 4000 ft
*bright light inside affects vision at night
how to manage with dim lights
- avoid bright white light (strobes, flashing, landing lights) 30 min before flying at night.
- avoid white light even inside the cockpit
- move your eyes 10 degrees to the side of an object, so that the light hits the rodes area more than the cones. Rodes help focus on objects in dim light
use red light in cockpit - it has less effects on the retina compared to green and bue
when switching from bright to dark - close one eye whilst the other is open
Vision -
What is accommodation
ability of the eye to focus on close and distant objects
ie. far to close/close to far
deteriorates with age and tiredness
what is myopia
Reflective Error due to shape of the eye or power of the lens
short sightedness
can focus up close but not far
need concave lense to fix
hyperopia
long sightedness
can focus at a distance but not close
(ie reading)
need convex lens to correct
Use of corrective lenses by pilots
Avoid using reading lenses because distant objects will be blurred
Use half moon lenses
Use bifocal lenses (not vifocal lenses)
Visual system is comprised of 2 things:
optic nerve + visual vortex
what’s the visual vortex
part in the brain responsible for processing info received by the eyes - processes motion, colour and shape
function of the tear duct
washes the surfaces of the eye with antibiotic solution.
needs to be kept moist to help oxygen difuse thru
and protect from damage from dust particles
visual acuity
capacity of the eye to resolve detail (depends on density of photoreceptors) depending on distance
12 megapixel resoultion vs 3megapixedl
with more distance, the less detail you can resolve
where can alpha neumeric info be resolved
in the fovea because it’s the part of the retina that can process visual detail
which part of the retina is better for resolving objects at night
rods that help with peripheral vision can detect movement of objectts in dim light or at night
what are the 2 movements of the eye
Saccade and pursuit movements
explain the movement of the eye
Saccades are directed towards stationary targets to align our visual axis to the object
pursuit is directed at moving targets
our eyes combine both movements with no conscious
eyes move by 6 muscles
Normal acuity
ability to see 20/20 (6/6)
in snellen chart, what does 20/40 mean?
a person is able to read the letters at a visual acuity of 20 feet compared to a normal person who can read it at 40 feet - this is a near sighted person
factors affecting Visual Acuity
which angle of the eye you are seeing from
dark conditions
age
disease
dead photoreceptors
hypoxia
smoking, drinking, medication
short/near sightedness
external conditions (dust, weather, water, or anything that physically obscures object)
why avoid photochromic sungalsses
don’t respond to changing light conditions, especially going from light to dark
they require UV light to function
why avoid polarised glasses
adds polarising effects on screens and displays which hinders your visibility
what is empty field myopia
if the eye has nothing to focus on, it resumes a default focus 1 - 2 metres.
if you are looking at distant threats, you will be unable to see them at first and must refocus
Look at distant objects in the environment, distant or at the horizon or even your wingtips - should do continuous scanning
Detecting objects in the dark
1) the more the pupil enlarges, the less focus it has. It puts a lot of reliance on the lense to adjust focus
2)we have less rods near the fovea so hard to see objects i the dark in central view, so you may have to look at objects from the side a bit where there are more rods
Tips for look out
- involve** a degree of frequent eye movement **to cover blind spots
BUT frequent eye movement might stop you from detecting ‘relevant movement’
- move attention to one erea, then keep still for a period (to help detected movement), then move to next area. Make sue that your vield of vision at each stop overlaps the previously searched area by 10 degrees
- **you can be on a collision course with another aircraft because there is no apparent relative motion between you and the other aircraft. Aircraft will get bigger and bigger.
If you are flying 100 knots and aircraft is fying 500knots, then the rate of closure is 600knots (10nn per min)
the time you see the other aircraft depends on when you see the aircraft and the rate of closure.
If you see the aircraft at 1nm, you have 1/10th of a minute (6 seconds)
if you see the aircraft at 3nm, you you have 18 seconds
- **look at distant objects **in straight direction for focus
- **avoid empty field myopia **by consciously look at distant objects like a cloud, a wing tip otherwise your eyes will only focus at 1-2 m ahead and miss a distant aircraft
*be aware that in hazy conditons aircrafts whose edges are blurry/unclear may appear further than they really are.
LOOK OUT AT NIGHT
- need to rely on peripheral vision
- scan the sky more slowly than daylight
- look at objects from the side 10-20 degrees
what is scotopic vision
distinguish light and dark - ie rods
photobic vision
ability to detect colour - cones
Color blindness (photopic)
Inability of detecting some colour due to imperfection in the cones or absense of hte cones - usually red and green
dangerous because you can’t see certain lights like nav lights or lights from ATC tower
Ishihara cards
to test colour blindness
Refractive errors
defect in shape of the eyeball or deffects in the power of the lens
here the plane of focus does not align with the retina, therefore need corrective lenses to bring the focus on the retina
Astigmatism
imperfection in the shape of the cornea or lens. Causes uneven refractions of rays
so results in different optical power in different areas of the cornea or lens
difficult to resolve detail - image is distorted
can be corrected by lenses
Symptoms of astigmatism
sometimes no symptoms
but with age it can become common
can cause headaches, blurred vision, lack of focus, squinting to focus